All Questions
32
questions
2
votes
0
answers
129
views
"Charlie" Sheen BRDF's directional albedo integrates to values higher than 1 at low roughnesses. Does this mean it is not energy conserving?
I am implementing the BRDF from the 2017 paper "Production Friendly Microfacet Sheen BRDF". This BRDF is modelled as a coat layer stacked on top of a base specular. In order to do so in an ...
- 53
1
vote
1
answer
247
views
Confusion over Microfacet-based BRDFs and Normal Distribution Functions
Through reading various sources online, I've become a bit confused. I'll briefly outline what I think I do understand:
My understanding is that microfacet-based BRDFs assume there is always a perfect ...
- 229
0
votes
0
answers
63
views
Unable to compute fresnel reflections properly
I am implementing fresnel reflections for materials in my renderer.
According to this source, here the look I should obtain when rendering a sphere over a grey background:
I have two implementations. ...
- 103
0
votes
1
answer
168
views
Does fresnel reflection make sense for metals?
I am implementing fresnel reflections for materials in my renderer.
Does it make sense for metals?
Here my implementation:
...
- 103
1
vote
1
answer
175
views
The purpose of NdotV in the directional-hemispherical reflectance equation in the book "Real-time rendering book"
I have been reading the book "real-time rendering 4th edition" and came across this Directional-hemispherical reflectance equation.
$$R(\mathbf{l}) = \int_{\mathbf{v}\in\Omega} f(\mathbf{l}, ...
1
vote
1
answer
66
views
Is the dichromatic model physically based?
lately I have been learning about photometry, and everywhere I look I see a BRDF written according to the "dichromatic model". Roughly speaking: $$\rho= \rho_D+\rho_S \cdot (...)$$
for some $...
- 113
1
vote
1
answer
151
views
Conflicting definitions for the distribution of normals $D$ in microfacet BSDFs
Please do not confuse this question with this one. In Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, Eric Heitz defines the distribution of normals as.
There, the footnote. ...
3
votes
1
answer
208
views
Confusion of deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper
When deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper:
First we have a macrosurface BSDF which is:
$f_{s}(\mathbf{i}, \mathbf{o}, \mathbf{n})=\int\left|\frac{\...
- 31
0
votes
1
answer
441
views
Path tracing: How to ensure we are sampling a direction vector within the visible hemisphere of a surface?
Given a surface Normal vector of an intersection point, how can one generate a random direction vector that is guaranteed to be in the visible hemisphere? The way I ...
- 241
0
votes
1
answer
322
views
BRDF for point lights should not return values over 1
This is standard Cook-Torrance BRDF in formulation for a single point light. No intergrals over a hemisphere, just a single direction to a source of incoming energy.
$$
L_o = { \bigg ( (1-F) \frac{...
- 193
1
vote
0
answers
70
views
How to handle negative reflection directions in raytracing?
I got a function that generates samples from a GGX visible normal distribution function. When I use it to calculate reflection directions obviously some of these intersect with the surface agin (...
- 11
1
vote
1
answer
1k
views
Roughness Value of (Close to) Zero in Physically Based Rendering
In my Direct Light Physically Based Renderer, when I set the roughness too low (ie. 0.0 or close) the specular reflection doesn't show, not even at high resolutions and at perfect angle with the ...
- 163
3
votes
1
answer
385
views
Strange dark spot when lighting in deferred rendering PBR shaders
It's probably something obvious but there seems to be a strange issue with lighting in my pipeline. I'm trying to keep everything in world space at the moment for simplicity but cannot figure out what'...
- 51
1
vote
0
answers
84
views
Questions about BRDF parameterization
Hi I'm trying to get a better understanding of the BRDF modeling. I only implemented naive diffuse(lambert), specular and microfacet BRDF before, but I don't have much experience in mixed BRDFs and ...
- 61
1
vote
0
answers
880
views
GGX BRDF is greater than 1?
I am implementing a GGX BRDF, this is the formula I used is from:https://schuttejoe.github.io/post/ggximportancesamplingpart1/
And this is my implementation:
...
- 187